A differential pressure gauge uses a U-shaped glass tube filled with liquid to measure pressure differences. The height difference of the liquid in the two arms indicates the pressure variation. The gauge can use denser fluids for larger pressure differences. Portable digital gauges use low freezing point, high-density indicator fluids and can be connected to computers for configuring results.
A simple differential pressure gauge consists of a U-shaped glass tube in which an inert liquid is placed. When the two U-shaped arms are subjected to different pressures, the fluids in the respective tubes reach different heights. The pressure variation from one place to another can be determined by the difference in height of the fluid in the two arms. Differential pressure gauges can range from devices simple enough to build at home to electronic equipment with computer chips and digital readouts.
When the openings at the top of a differential pressure gauge are exposed to the same pressure, such as atmospheric pressure, the liquid in the arms is at the same height. When another pressure is to be measured, such as the air pressure in a SCUBA tank, the air pressure in the tank will push the fluid in the attached arm down, while the fluid in the opposite arm rises.
To calculate the pressure difference between atmospheric air and tank air, the difference between the height of the fluid in each arm is measured. Larger pressure differences are measured using denser fluids, such as mercury, while smaller pressure differences can be obtained with less dense fluids, such as water.
When a meteorologist talks about a barometric pressure of so many millimeters (mm) of mercury, it may mean that the pressure difference between the inside and outside of a storm will push mercury up a differential pressure gauge tube by that amount. For example, atmospheric pressure, 14.7 pounds per square inch (about 101 kPa), will push the mercury up a 30-inch (760 mm) pipe, while the water will rise 33 feet. The eye of a category five hurricane at 13.3 psi (about 93 kPa) will push the mercury up 690 mm, but the water will rise 29.8 feet. The water rises much higher than the heavier mercury in the arm of the U-shaped tube, and so a simple water pressure gauge would be much larger than one that uses mercury. The pressure difference can be measured by multiplying the weight of the fluid column by its change in height.
A portable differential pressure gauge must use mercury and other low freezing point, high density indicator fluids. Portable digital differential pressure gauges have two external valves, each of which can be connected to a pressure source. Battery operated digital gauges are push button activated to produce readings in several formats. Cables are available to connect portable units to computers for configuring results and designing reports.
Protect your devices with Threat Protection by NordVPN
